3.5mm line-in with separate monitor? Splitter recommendations?

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Recently bought a Razer Blade 15 Advanced. I've been using a self-built desktop with multiple 3.5mm line-in ports. My current setup uses a pre-amp that connects 3.5mm to 3.5mm into the desktop. I monitor all system sound with a 3.5mm headset plugged into a headphone jack on the desktop. Any recommendations for moving this setup to the Razer laptop? There's only one 3.5mm port, which I currently use for the headphones. I've tried using a Dell Thunderbolt dock with a 3.5mm line-in port, but although the other features on the dock work (e.g. monitors, USB) the 3.5mm audio line-in doesn't seem to be detected by the Razer. I'm wondering if a 3.5mm splitter would allow line-in and headphone out on the same port? (My current solution is to use a RODE Wireless Go II, with the 3.5mm going into the TX and the TR running via USB C into the RAZER...The TR gets power over that connection, but the TX just burns battery the whole time.)